This invention relates to fluorine and acrylic modified silicone resin useful in powder coatings and particularly to a process and composition based on sequential reaction of a coreative fluorinated compound with silicone resin followed by coreaction with a reactive acrylic polymer.
Acrylic resins are known to be useful in powder coatings and to exhibit good weathering properties if the acrylic polymer does not contain appreciable amounts of copolymerized styrene. Acrylic copolymers of silicone resin should provide substantially improved weathering properties with silicone resins. However, attempting to coreact acrylic copolymers with silicone resins is difficult to achieve in practice since the reaction is difficult to control and often results in cross-linked polymers known as gels. The reaction is difficult to control due to hydroxyl groups or other functional groups on the acrylic polymer as well as the preponderance of hydroxyl groups or alkyl ether groups on silicone resin, which coreact to cause a gel during synthesis or subsequently during a solvent stripping step.
It now has been found that step-wise synthesis of a fluorinated-silicone-acrylic copolymer resin provides superior weatherability properties as well as advantageously avoiding the gellation problem occurring in the formation of acrylic-silicone polymers. In accordance with this invention, the fluorinated-silicone-acrylic terpolymer is produced in step-wise processing, wherein the silicone resin is first reacted with a fluorinated reactant such as fluorinated alcohol to produce a fluorinated silicone resin followed by reaction with a hydroxylated acrylic polymer to form a fluorinated-silicone-acrylic resin. The hydroxylated acrylic polymer can be preformed or formed in-situ in the presence of the fluorinated-silicone resin. The resulting polymer is particularly useful as a polymeric binder in powder coatings and forms a film in use particularly exhibiting superior weathering properties as well as other advantageous film integrity properties. These and other advantages of this invention will become more apparent by referring to the detailed description and illustrative examples.